Antenna device

ABSTRACT

Provided is an antenna device which is small and low in height to be easily mounted on a small radio and forms a main beam, which has excellent radiation pattern frequency characteristics and is tilted in the horizontal direction. Slot elements ( 103   a,    103   b ) of an antenna ( 101 ) are excited with a phase difference (d). A reflection plate ( 105 ) is provided with a plurality of patch elements ( 107 ) having a resonance frequency higher than the center frequency of the antenna ( 101 ), and a plurality of patch elements ( 108 ) having a resonance frequency lower than the center frequency of the antenna ( 101 ) around the patch elements ( 107 ).

TECHNICAL FIELD

The present invention relates to an antenna apparatus. For example, thepresent invention is suitable for use as a stationary radio apparatusand radio terminal apparatus in high-speed radio communication systems.

BACKGROUND ART

In high-speed radio communication systems such as wireless LAN systems,it is necessary to take measures against multipath fading and shadowingto realize high-speed transmission. A sector antenna is studied as oneof the measures. A sector antenna aligns a plurality of antenna elementswhere the main beams are directed in different directions, andselectively switches a plurality of antenna elements depending on radiopropagation environments.

Generally, antennas installed in stationary radio apparatuses mounted inceilings and radio terminal apparatuses for notebook computers used ondesks are requested to have a flat structure and a small size from theviewpoint of productivity and portability. Further, from the viewpointof indoor communication environment, the directivity of these antennaspreferably tilts the angles of elevations of main beams horizontallyfrom the vertical direction with respect to the antenna face.

Up to now, as this kind of antennas, a sector antenna using a loopantenna is proposed as disclosed in Patent Document 1. This sectorantenna is configured by aligning a plurality of loop antennas havingconductors in a folded shape on a plane at a given distance from a platereflector. A loop antenna is formed by connecting conductors in a foldedshape and by placing a plate reflector, so that it is possible to formmain beams tilted in a horizontal direction and, furthermore, it ispossible to switch the main beam direction by switching feedingpositions. In this way, one loop antenna realizes beams in twodirections, so that features of the sector antenna include the footprintsmaller.

Further, as another antenna, a sector antenna using slot elements isproposed as disclosed in Patent Document 2. This sector antenna isconfigured by placing four slot elements at a given distance from aplate reflector, so that features of the sector antenna include a simpleconfiguration and a very small footprint. By arranging the four slotelements in a square shape and by feeding two opposing slot elementswith a phase difference, main beams tilted in a horizontal direction areformed. Further, by switching the phase differences, the main beams canbe switched to the opposite direction, so that it is possible to formmain beams in four directions by four slot elements arranged in a squareshape.

By the way, there is a problem with the sector antennas disclosed inPatent Documents 1 and 2 that the distance to the plate reflector needsat least ¼ wavelength or greater although the footprint can be made verysmall. For example, in the case of a 5 GHz operating frequency, thedistance to the plate reflector needs at least 25 mm or greater.Considering the sector antenna is mounted in a radio apparatus, thisthickness prevents miniaturization, and the distance to the platereflector is preferably as narrow as possible.

As a technique for making a low-profile antenna that makes a radiationdirection a single direction using a plate reflector, EBG(Electromagnetic BandGap) structure adopting a plate reflector isproposed up to now.

As this kind of antennas, a dipole antenna placed on an EBG platereflector is proposed as disclosed in Non-patent Document 1. Accordingto this document, even in a very low-profile antenna configuration ofplacing a dipole antenna a 0.04 wavelength apart from an EGB platereflector on which a plurality of patch elements are arranged, it ispossible to realize impedance matching and obtain good unidirectionalradiation characteristics.

Further, as another antenna, a spiral antenna placed on an EBG platereflector is proposed as disclosed in Non-patent Document 2. Accordingto this document, by placing a spiral antenna a 0.06 wavelength apartfrom an EGB plate reflector on which a plurality of patch elements arearranged, it is possible to make low-profile without damaging circularpolarized wave characteristics.

Further, as another antenna, a two-frequency antenna placed on an EBGplate reflector is proposed as disclosed in Non-patent Document 3. Inthis two-frequency antenna, two orthogonal dipole antennas are placed ata very narrow interval on an EBG plate reflector on which a plurality ofrectangle patch elements are arranged. By this means, the dipoleantennas placed in parallel on the short side of the patch elementoperate as antennas for a high frequency band, and the dipole antennasplaced in parallel on the long side of the patch element operate asantennas for a low frequency band. As a result, it is possible tosuppress the deterioration of efficiency of radiation caused by aclosely placed plate reflector and realize a wideband two-frequencyantenna.

Further, as another antenna, a phased dipole array antenna placed on anEBG plate reflector is proposed as disclosed in Non-patent Document 3.According to this document, by placing a phase dipole array antenna a0.14 wavelength a part from the surface of an EGB plate reflector onwhich a plurality of patch elements are arranged, it is possible torealize a low-profile antenna having main beams tilted in a horizontaldirection.

-   Patent Document 1: Japanese Patent Application Laid-Open No.    2005-72915-   Patent Document 2: Japanese Patent Application Laid-Open No.    2005-269199-   Patent Document 3: Japanese Patent Application Laid-Open No.    2005-94360-   Non-patent Document 1: IEEE Trans. Antennas Propagat., vol. 51, no.    10, pp. 2691-2703, October 2003.-   Non-patent Document 2: Proc. Antennas and Propagation Soc. Int.    Symp., vol. 1, pp. 831-834, June 2004.-   Non-patent Document 3: IEICE general conference, 2006, B-1-63

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

Although the dipole antenna disclosed in Non-patent Document 1, thespiral antenna disclosed in Non-patent Document 2, the two-frequencyantenna disclosed in Non-patent Document 3 and the phased dipole arrayantenna disclosed in Non-patent Document 3 are realized by using an EBGplate reflector on which a plurality of patch elements are aligned, noconsideration is given to the frequency characteristics of radiationpatterns. The frequency characteristic of radiation patterns is one ofimportant characteristics in the case of applying an antenna to radiocommunication systems, and, as shown in the above documents, when an EBGplate reflector is adopted in an antenna, by resonation characteristicsof patch elements, the radiation patterns are more likely to showfrequency characteristics.

It is therefore an object of the present invention to provide an antennaapparatus that is small and low-profile so as to be installed easily ina small radio apparatus, that has radiation patterns of good frequencycharacteristics and that can form main beams with a tilt in a horizontaldirection.

Means for Solving the Problem

According to an aspect of the antenna apparatus of the presentinvention, an antenna apparatus adopts a configuration including: aplate reflector that includes: a first plate conductor formed of ametallic material; a plurality of first conductor elements provided at agiven distance from the first plate conductor; a plurality of secondconductor elements aligned around the plurality of first conductorelements; and a connection conductor that connects electrically eachcenter of the plurality of first conductor elements and each center ofthe plurality of second conductor elements with the first plateconductor; and a first and second radiation sources that are provided ona side of the plurality of first conductor elements and the plurality ofsecond conductor elements at a given interval from the plate reflectorand that are excited with a phase difference between the first andsecond radiation sources.

Further, according to an aspect of the antenna apparatus of the presentinvention, the antenna apparatus adopts a configuration including: theplate reflector has an electromagnetic bandgap structure, in which theplurality of first and second conductor elements have resonancecharacteristics in a first and second frequency bands, respectively; andthe first frequency band is set higher than the second frequency band.

According to these configurations, it is possible to realize a small andlow-profile antenna apparatus that has radiation patterns of goodfrequency characteristics and that can form a main beam tilted in ahorizontal direction.

Further, according to an aspect of the antenna apparatus of the presentinvention, in the above configuration, the first radiation source andthe second radiation source include a first slot element and a secondslot element formed in parallel on the second plate conductor, and,further, the antenna apparatus adopts a configuration including: a thirdslot element that is formed in the second plate conductor such that thethird slot element is orthogonal to the first slot element; and a fourthslot element that is formed in the second plate conductor at the giveninterval from the third slot element in parallel, wherein the third andthe fourth slot elements are excited with the phase difference betweenthe third element and the fourth element.

Further, according to an aspect of the antenna apparatus of the presentinvention, the first radiation source and second radiation sourceinclude a first dipole element and a second dipole element placed inparallel, and, further, the antenna apparatus adopts a configurationincluding: a third dipole element that is placed such that the thirddipole element is orthogonal to the first dipole element; and a fourthdipole element that is placed at the given distance from the thirddipole element in parallel, wherein the third and the fourth dipoleelements are excited with the phase difference between the third dipoleantenna and the fourth dipole antenna.

According to these configurations, it is possible to realize amulti-sector antenna apparatus in four directions that is small andlow-profile, and that has radiation patterns of good frequencycharacteristics.

Advantageous Effect of the Invention

According to the present invention, it is possible to realize an antennaapparatus that is small and low-profile, and forms main beams with atilt in a horizontal direction and that has radiation patterns of goodfrequency characteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a perspective view showing the configuration of the antennaapparatus according to Embodiment 1 of the present invention;

FIG. 1B is a side view showing the configuration of the antennaapparatus according to Embodiment 1;

FIG. 2 is a plane view showing the antenna configuration;

FIG. 3 is a plane view showing the configuration of the plate reflector;

FIG. 4 shows characteristics of the plate reflector of the antennaapparatus according to Embodiment 1;

FIG. 5 shows the directivity of the antenna apparatus according toEmbodiment 1;

FIG. 6A is a perspective view showing the configuration of the antennaapparatus as a comparison example against Embodiment 1;

FIG. 6B is a side view showing the configuration of the antennaapparatus as a comparison example against Embodiment 1;

FIG. 7 shows the directivity of the antenna apparatus of FIGS. 6A and6B;

FIG. 8A is a perspective view showing the configuration of the antennaapparatus as a comparison example against Embodiment 1;

FIG. 8B is a side view showing the configuration of the antennaapparatus as a comparison example against Embodiment 1;

FIG. 9 shows the directivity of the antenna apparatus of FIGS. 8A and8B;

FIG. 10A shows radiation characteristics between the antenna apparatusof Embodiment 1 and the antenna apparatus of a comparison example;

FIG. 10B shows radiation characteristics between the antenna apparatusof Embodiment 1 and the antenna apparatus of a comparison example;

FIG. 11A is a perspective view showing the configuration of the antennaapparatus according to Embodiment 2;

FIG. 11B is a cross-sectional view showing the configuration of theantenna apparatus according to Embodiment 2;

FIG. 12 is a plane view showing the configuration of the platereflector;

FIG. 13 shows the directivity of the antenna apparatus according toEmbodiment 2;

FIG. 14A shows radiation characteristics between the antenna apparatusof Embodiment 2 and the antenna apparatus of a comparison example;

FIG. 14B shows radiation characteristics between the antenna apparatusof Embodiment 2 and the antenna apparatus of a comparison example;

FIG. 15A is a perspective view showing the configuration of the antennaapparatus according to Embodiment 3;

FIG. 15B is a side view showing the configuration of the antennaapparatus according to Embodiment 3; and

FIG. 16 shows the directivity of the antenna apparatus according toEmbodiment 3.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described in detailwith reference to the accompanying drawings. Further, the same numeralsare assigned to components having the same configurations or functionsin the figures and the description thereof will not be repeated.

Embodiment 1

The antenna apparatus according to Embodiment 1 of the present inventionwill be described using FIGS. 1 to 10. FIG. 1A is a perspective viewshowing the configuration of the antenna apparatus according toEmbodiment 1 of the present invention. FIG. 1B is a side view showingthe configuration of the antenna apparatus, that is, a view seen fromthe −Y side in FIG. 1A. FIG. 2 is a plane view of antenna 101 of FIGS.1A and 1B, seen from the +Z side in FIG. 1B. FIG. 3 is a plane view ofplate reflector 105 shown in FIGS. 1A and 1B, seen from the +Z side inFIG. 1A.

Antenna apparatus 100 has antenna 101 and plate reflector 105. Antenna101 and plate reflector 105 are placed given distance h apart as knownfrom FIG. 1B.

Plate reflector 105 has: ground conductor 110 as a first plate conductorformed of a metallic material; patch elements 107 as a plurality offirst conductor elements placed at a given distance from the first plateconductor; patch elements 108 as a plurality of second conductorelements aligned around a plurality of first conductor elements; andthrough hole 109 as a connection conductor for connecting electricallyeach center of a plurality of first conductor elements and each centerof a plurality of second conductor elements with the first plateconductor.

Further, according to the present embodiment, plate reflector 105 has anEBG (Electromagnetic BandGap) structure where a plurality of patchelements 107 and 108 have resonance characteristics in the first andsecond frequency bands, respectively. In addition, patch elements 107and 108 are configured such that the first frequency band is higher thanthe second frequency band.

Antenna apparatus 100 according to the present embodiment such that aplurality of patch elements 107 and 108 have an EBG structure havingresonance characteristics in a first and second frequency bands and, inorder to make the first frequency band higher than the second frequencyband in this way, several efforts are made to antenna apparatus 100. Theconfigurations will be described later in detail.

Antenna 101 is placed on the side of patch elements 107 and 108 fromplate reflector 105 at given distance h. Slot elements 103 a and 103 bas first and second radiation sources excited with a phase differencebetween them are provided on antenna 101.

Slot elements 103 a and 103 b are formed by cutting copper foil on thesurface of dielectric substrate 102. Dielectric substrate 102 is adielectric substrate having a relative permittivity εr of, for example,2.6 and thickness t1, and its plane shape is a Lg×Lg square.

Slot elements 103 a and 103 b as first and second radiation sourceshaving a length of Ls and a width of Ws, are aligned parallel at elementinterval d and excited by feed points 104 a and 104 b, respectively. Atthis time, feed points 104 a and 104 b are excited having phasedifference δ (i.e. the phase at feed point 104 b—the phase at feed point104 a). Although a case has been explained where slot elements 103 a and103 b are directly excited by feed points 104 a and 104 b, a microstripline may be formed on the rear face of dielectric substrate 102 and theslot elements may also be excited by electromagnetic field coupling.Antenna 101 configured in this way is placed at given distance h fromthe surface of plate reflector 105 (i.e. the +Z plane).

In plate reflector 105, a plurality of patch elements 107 and 108 areformed on the surface of dielectric substrate 106, and the center partsof the patch elements 107 and 108 are individually connected with groundconductor 110 formed on the rear face of dielectric substrate 106 viathrough holes 109. Dielectric substrate 106 is a double-sided,copper-clad, dielectric substrate having a relative permittivity εr of,for example, 2.6 and a thickness of t2, and its plane shape is a Lr×Lrsquare.

Patch element 107 is a conductor with sides of a length of Wp and placedin the center part of plate reflector 105, that is, immediately belowand close to antenna 101. A square notch with sides of a length of s1 isformed in each vertex of the conductor. Patch element 108 is a conductorwith sides of a length of Wp and placed so as to surround the perimeterof patch elements 107. A slit of s2×s3 is each formed in the center ofthe sides of the conductor. N×N patch elements 107 and 108 are arrangedat element interval G between the elements. By configuring platereflector 105 in this way, it is possible to regard the plate reflectoras an equivalent to a parallel LC resonant circuit.

FIG. 4 shows the reflection phases of patch elements 107 and 108 in acase where patch elements 107 and 108 are periodically arranged in twodimensions and where a plane wave enters patch elements 107 and 108 fromthe front direction. Reflection phase characteristics 401 and 402 showthe reflection phase characteristics of patch elements 107 and 108,respectively. The reflection phase in FIG. 4 is assumed a case wherethickness t2 of dielectric substrate 106 is a 0.027 wavelength, thelength Wp of a side of a patch element is a 0.23 wavelength, elementinterval G is a 0.017 wavelength, s1 is a 0.025 wavelength, s2 is a0.058 wavelength, and s3 is a 0.017 wavelength. The reflection phase iszero degree upon resonance, and the surface of the plate reflector is inthe same condition as a perfect magnetic conductor. In FIG. 4, it isevident from reflection phase characteristic 401 that patch element 107resonates with a higher frequency than center frequency fc of antenna101, and it is evident from reflection phase characteristic 402 thatpatch element 108 resonates with a lower frequency than center frequencyfc of antenna 101. If patch elements 107 and 108 each have a squareshape with sides of a length of a 0.23 wavelength without notches orslits, resonate with center frequency fc of antenna 101.

FIG. 5 shows the directivity on the vertical (XZ) plane where distance his a 0.125 wavelength. The directivity of FIG. 5 is shown in a casewhere antenna 101 and plate reflector 105 are configured as follows. Asfor antenna 101, thickness t1 and dimension Lg of antenna 101 are a0.027 wavelength and a 0.77 wavelength, respectively, length Ls of slotelements 103 a and 103 b are a 0.27 wavelength, width Ws is a 0.017wavelength, element interval d is a 0.33 wavelength and phase differenceδ is 70 degrees. As for plate reflector 105, 6×6 patch elements 107 arearranged in the center, that is, near antenna 101, and patch elements108 are aligned every two elements around patch elements 107 (i.e. N=10)and total dimension Lr of plate reflector 105 is 2.48 wavelengths. Thedimensions of patch element 107 and patch element 108 are the samevalues as described above.

In FIG. 5, directivity 501 to 503 shows the directivity of vertical Eθpolarized wave component when the operating frequencies are a 0.98 fc, a1.02 fc and a 1.06 fc, respectively, and it is evident that the mainbeams tilted in the direction of 35 degree elevation angle θ areobtained in any frequencies. Further, it is possible to check smallchanges in the radiation patterns with respect to the frequencies.

Now, as comparison example 1 with respect to the present embodiment, acase where the resonance frequency of all patch elements is fc, that is,a case where the patch element is a square shape with sides of a lengthof a 0.23 wavelength, will be described. FIG. 6A is a perspective viewshowing the configuration of the antenna apparatus where all patchelements 602 formed on plate reflector 601 are square shapes. FIG. 6B isa side view of the antenna apparatus seen from the −Y direction in FIG.6A. Plate reflector 601 is configured by arranging 10×10 patch elements602 each having a square shape with sides of a length of a 0.23wavelength at element interval G of a 0.017 wavelength. That is, thisplate reflector is the same configuration as the plate reflector wherepatch elements 107 and 108 in the present embodiment are formed withoutnotches and slits.

FIG. 7 shows the directivity on the vertical (XZ) plane where distance his a 0.125 wavelength in the configuration shown in FIGS. 6A and 6B.Directivity 701 to 703 shows the directivity of vertical Eθ polarizedwave component when the operating frequencies are a 0.98 fc, a 1.02 fcand a 1.06 fc, respectively. By the frequency characteristic ofreflection phase in plate reflector 601, it is evident that theradiation patterns with respect to the frequencies change significantly.

Now, as comparison example 2 with respect to the present embodiment, acase where the plate reflector is a metallic conductor will bedescribed. FIG. 8A is a side view showing the configuration of theantenna apparatus where the plate reflector is a metallic conductor andFIG. 8B is a side view of the antenna apparatus seen from the −Ydirection in FIG. 8A. FIG. 9 shows the directivity on the vertical (XZ)plane where distance h is a 0.33 wavelength in the configuration shownin FIGS. 8A and 8B. Directivity 901 to 903 shows the directivity ofvertical Eθ polarized wave component when the operating frequencies area 0.98 fc, a 1.02 fc and a 1.06 fc, respectively. Similar to theconfiguration of the present embodiment shown in FIGS. 1A and 1B, it isevident that the main beams tilted in the direction of 35 degreeelevation angle θ are obtained in any frequencies. Further, platereflector 801 does not have frequency characteristics, so that changesare little in the radiation patterns with respect to the frequencies.

FIGS. 10A and 10B show frequency characteristics of the tilt angles andgains between antenna apparatus 100 of the present embodiment (FIGS. 1Aand 1B), the antenna apparatus of comparison example 1 (FIGS. 6A and 6B)and the antenna apparatus of comparison example 2 (FIGS. 8A and 8B). InFIGS. 10A and 10B, characteristics 1001 and 1004 show the frequencycharacteristics of the tilt angle and the gain where distance h in FIG.1B is a 0.125 wavelength in antenna apparatus 100 of the presentembodiment, characteristics 1002 and 1005 show the frequencycharacteristics of the tilt angle and the gain where distance h in FIG.6B (comparison example 1) is a 0.125 wavelength, and characteristics1003 and 1006 show the frequency characteristics of the tilt angle andthe gain where distance h in FIG. 8B (comparison example 2) is a 0.33wavelength. It is evident from FIG. 10A that, in characteristic 1001 ofantenna apparatus 100 of the present embodiment, a change in the tiltangle is less than in characteristic 1002 of comparison example 1, andalmost the same tilt angle is obtained as characteristic 1003 ofcomparison example 2 although the distance to the plate reflector isnarrower than in comparison example 2. Further, as for the gain shown inFIG. 10B, changes are little in the frequencies in all of theconfigurations.

In this way, according to the present embodiment, in a tilt beam antennaconfigured with two slot elements and a plate reflector, a plurality ofpatch elements 107 having a higher resonant frequency than the centerfrequency of antenna 101 and a plurality of patch elements 108, whichare arranged around patch elements 107, and which have a lower resonantfrequency than the center frequency of antenna 101, are provided onplate reflector 105, so that it is possible to realize low-profiletilted beam antenna apparatus 100 that has radiation patterns of goodfrequency characteristic.

Although a case has been explained with the present embodiment about theconfiguration of the antenna that feeds with a phase difference two slotelements 103 a and 103 b at a given interval, the same effect may beobtained as a linear element configuration such as a dipole antenna.Further, the same effect may be applied by using an antenna having twocurrent peaks with various phase differences in one element. That is, anantenna may need to be configured by providing the first and secondradiation sources on the side of a plurality of first and secondconductor elements of the plate reflector at a given interval, and byexciting the radiation sources with a phase difference each other.

Further, although a case has been explained with the present embodimentwhere the patch element is a square shape, the same effect may beapplied to a circular shape or a regular polygon.

Embodiment 2

The antenna apparatus according to Embodiment 2 of the present inventionwill be explained using FIGS. 11 to 14. FIG. 11A is a perspective viewshowing the configuration of the antenna apparatus according toEmbodiment 2 of the present invention. FIG. 11B is a cross-sectionalview showing the configuration of the antenna apparatus, that is, a viewof near the center of antenna apparatus 200 along the X axis in FIG.11A, seen from the −Y side. FIG. 12 is a plane view of plate reflector1101 shown in FIGS. 11A and 11B, seen from the +Z side in FIG. 11A.

Referring to these figures, in plate reflector 1101, a plurality ofpatch elements 107 and 1103 are formed on the surface of dielectricsubstrate 1102, and the center parts of the patch elements 107 and 1103are individually connected with ground conductor 110 formed on the rearface of dielectric substrate 1102 via through holes 109.

Dielectric substrate 102 is a dielectric substrate having a concaveshape having a relative permittivity εr of, for example, 2.6, thicknesst3 of the part where patch elements 107 arranged immediately below ornear antenna 101 are formed, and thickness t4 (greater than t3) of thepart where patch elements 1102 are formed.

Patch element 1103 is a square conductor with sides of a length of Wpand which is formed around patch elements 107. The reflection phasewhere patch elements 1103 are periodically arranged in two dimensionsand a plane wave enters the patch elements from the front direction, isat zero degree, that is, the patch elements resonate at higher frequencythan a case where patch elements 107 are periodically arranged and thancenter frequency fc of antenna 101.

These N×N patch elements 107 and 1103 are arranged at element interval Gbetween the patch elements, and sides of a length of entire platereflector 1101 are Lr2×Lr2. Antenna 101 is placed above plate reflector1101 configured in this way at distance h from the face forming patchelement 107.

FIG. 13 shows the directivity on the vertical (XZ) plane where distanceh is a 0.125 wavelength. The directivity of FIG. 13 is a case wherethicknesses t3 and t4 of dielectric substrate 1102 are 0.027 and 0.042wavelengths, the dimension Lr2 is 2.48 wavelengths, 6×6 patch elements107 are arranged, patch elements 1103 are aligned every two elementsaround patch elements 107 (i.e. N=10).

In FIG. 13, directivity 1301 to 1303 show the directivity of vertical Eθpolarized wave component when the operating frequencies are a 0.98 fc, a1.02 fc and a 1.06 fc, respectively, and it is evident that the mainbeams tilted in the direction of 35 degree elevation angle θ areobtained in any frequencies. Further, it is possible to check smallchanges in the radiation patterns with respect to the frequencies.

FIGS. 14A and 14B show frequency characteristics of the tilt angles andgains between antenna apparatus 200 of the present embodiment (FIGS. 11Aand 11B), the antenna apparatus of comparison example 1 (FIGS. 6A and6B) and the antenna apparatus of comparison example 2 (FIGS. 8A and 8B).In FIGS. 14A and 14B, characteristics 1401 and 1402 show the frequencycharacteristics of the tilt angle and the gain where distance h in FIG.11B is a 0.125 wavelength in antenna apparatus 200 of the presentembodiment. It is evident from FIG. 14A that, in characteristic 1401 ofantenna apparatus 200 of the present embodiment, a change in the tiltangle is less than in characteristic 1002 of comparison example 1, andalmost the same tilt angle is obtained as characteristic 1003 ofcomparison example 2 although the distance to the plate reflector isnarrower than in comparison example 2. Further, as for the gain shown inFIG. 14B, changes are little in frequencies in any configurations.

In this way, according to the present embodiment, in the tilt beamantenna configured with two slot elements and a plate reflector, platereflector 1101 is configured such that a plurality of patch elements 107and 1103 are arranged on concave-shaped dielectric substrate 1102, sothat, as in Embodiment 1, it is possible to realize low-profile tiltedbeam antenna apparatus 200 that has radiation patterns of good frequencycharacteristics.

Although a case has been explained with the present embodiment wherenotches are provided with patch element 107 arranged in the center partof plate reflector 1101, it is possible to increase the resonantfrequency difference between patch element 107 in the center part ofplate reflector 1101 and patch element 1103 around plate reflector 1101by increasing the difference between the thickness of the center ofdielectric substrate 1102 and the thickness of the surrounding even ifnotches are not provided, so that it is possible to obtain the sameeffect as the present embodiment.

Further, although a case has been explained with the present embodimentwhere plate reflector 1101 is configured by concave-shaped dielectricsubstrate 1102, even when a dielectric substrate has the same thickness(i.e. flat plate) and when the relative permittivity varies between thecenter of the dielectric substrate and around the dielectric substrate,so that it is possible to obtain the same effect as the presentembodiment.

Embodiment 3

The antenna apparatus according to Embodiment 3 of the present inventionwill be explained using FIGS. 15 and 16. FIG. 15A is a perspective viewshowing the configuration of the antenna apparatus according toEmbodiment 3 of the present invention. FIG. 15B is a side view showingthe configuration of the antenna apparatus, that is, a view seen fromthe −Y side in FIG. 15A.

Antenna apparatus 300 of the present embodiment is different fromantenna apparatus 100 of Embodiment 1 in the configuration of antenna1501. Antenna 1501 has slot elements 103 a, 103 b, 1502 a and 1502 bformed from cutting copper foil on the surface of dielectric substrate102. Slot elements 1502 a and 1502 b face each other such that slotelements 1502 a and 1502 b are orthogonal to slot elements 103 a and 103b. That is, slot elements 103 a, 103 b, 1502 a and 1502 b are aligned ina square shape.

Slot elements 103 a and 103 b are fed with a phase difference (phasedifference δ1=the phase at feed point 104 b—the phase at feed point 104a) by feed points 104 a and 104 b, respectively. At this time, feedpoints 1503 a and 1503 b are short-circuited. Similarly, slot elements1502 a and 1502 b are fed with a phase difference (phase differenceδ2=the phase at feed point 1503 b—the phase at feed point 1503 a) byfeed points 1503 a and 1503 b, respectively, and at this time, feedpoints 104 a and 104 b are short-circuited.

FIG. 16 shows the directivity of antenna apparatus 300, where distance hshown in FIG. 15B is a 0.125 wavelength, and the directivity of aconical plane at the elevation angle of 35 degrees. Directivity 1601shows the directivity of vertical Eθ polarized wave component when slotelements 103 a and 103 b are excited at 70 degree phase difference δ1,and it is possible to check that the main beam is directed to the +Xdirection. Similarly, directivity 1602 shows the directivity of verticalEθ polarized wave component when slot elements 103 a and 103 b areexcited at −70 degree phase difference δ1. Directivity 1603 shows thedirectivity of vertical Eθ polarized wave component when slot elements1502 a and 1502 b are excited at 70 degree phase difference δ2, anddirectivity 1604 shows the directivity of vertical Eθ polarized wavecomponent when slot elements 1502 a and 1502 b are excited at −70 degreephase difference δ2. Accordingly, it is possible to check that the mainbeams are directed to the −X direction, the +Y direction and the −Ydirection, respectively. In this way, by switching exciting slotelements and by switching excitation phases, it is possible to formbeams in four directions.

In this way, according to the present embodiment, in a tilted beamantenna configured by four slot elements and a plate reflector, aplurality of patch elements 107 having a higher resonant frequency thanthe center frequency of antenna 101 and a plurality of patch elements108, which are arranged around patch elements 107, and which have alower resonant frequency than the center frequency, are provided onplate reflector 105, and four slot elements 103 a, 103 b, 1502 a and1502 b are aligned in a square shape and facing slot elements areexcited with a phase difference. By this means, it is possible torealize low-profile, small-footprint and four-direction multi-sectorantenna apparatus 300.

INDUSTRIAL APPLICABILITY

The antenna apparatus according to the present invention provides anadvantage of forming a main beam tilted in a horizontal direction, andrealizing a small and low-profiled antenna having radiation patterns ofgood frequency characteristics and having a simple configurationsuitable for implementing in miniaturized radio apparatus, and isapplicable to a stationary radio apparatus and a radio terminalapparatus in high speed radio communication systems.

1. An antenna apparatus comprising: a plate reflector that comprises: afirst plate conductor formed of a metallic material; a plurality offirst conductor elements provided at a given distance from the firstplate conductor; a plurality of second conductor elements aligned aroundthe plurality of first conductor elements; and a connection conductorthat connects electrically each center of the plurality of firstconductor elements and each center of the plurality of second conductorelements with the first plate conductor; and a first and secondradiation sources that are provided on a side of the plurality of firstconductor elements and the plurality of second conductor elements at agiven interval from the plate reflector and that are excited with aphase difference between the first and second radiation sources.
 2. Theantenna apparatus according to claim 1, wherein: the plate reflector hasan electromagnetic bandgap structure, in which the plurality of firstand second conductor elements have resonance characteristics in a firstand second frequency bands, respectively; and the first frequency bandis set higher than the second frequency band.
 3. The antenna apparatusaccording to claim 2, wherein: the plurality of first conductor elementsand the plurality of second conductor elements are patch elements insquare shapes; and the first frequency band is set higher than thesecond frequency band by providing a notch in at least one vertex insaid each first element.
 4. The antenna apparatus according to claim 2,wherein: the plurality of first conductor elements and the plurality ofsecond conductor elements are patch elements in square shapes; and thefirst frequency band is set higher than the second frequency band byproviding a slit in at least one side of said each first element.
 5. Theantenna apparatus according to claim 2, wherein, the first frequencyband is set higher than the second frequency band by making a distancebetween the plurality of first conductor elements and the first plateconductor narrower than a distance between the plurality of secondconductor elements and the second plate conductor.
 6. The antennaapparatus according to claim 1, wherein the first radiation source andthe second radiation source comprise a first slot element and a secondslot element formed in parallel on the second plate conductor.
 7. Theantenna apparatus according to claim 1, wherein the first radiationsource and second radiation source comprise a first dipole element and asecond dipole element placed in parallel.
 8. The antenna apparatusaccording to claim 6, further comprising: a third slot element that isformed in the second plate conductor such that the third slot element isorthogonal to the first slot element; and a fourth slot element that isformed in the second plate conductor at the given interval from thethird slot element in parallel, wherein the third and the fourth slotelements are excited with the phase difference between the third elementand the fourth element.
 9. The antenna apparatus according to claim 7,further comprising: a third dipole element that is placed such that thethird dipole element is orthogonal to the first dipole element; and afourth dipole element that is placed at the given distance from thethird dipole element in parallel, wherein the third and the fourthdipole elements are excited with the phase difference between the thirddipole antenna and the fourth dipole antenna.